Method, system and apparatus for hybrid optical and electrical pumping of semiconductor lasers and leds for improved reliability at high temperatures

ABSTRACT

A method, system and an apparatus for hybrid optical and electrical pumping of semiconductor lasers and light-emitting diodes (LEDs) improves reliability at high operating temperatures. The semiconductor laser or LED is biased via optical pumping and a relatively small electrical modulation current modulates the laser. At low modulation speeds, the modulation current is substantially lower than that required for biasing the laser or directly modulating it at high speeds. The lifetime of the laser is improved by substantially reducing the operating current, enabling laser lifetimes adequate for operation in many applications, such as deep-hole oil drilling and jet engine control, where operation is not currently possible.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 61/747,298 entitled “Method and Apparatus for Hybrid Optical and Electrical Pumping of Semiconductor Lasers and LEDs for Improved Reliability at High Temperatures” filed Dec. 29, 2012. The above-referenced provisional application is hereby incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

This invention relates to laser modulation and reliability particularly for operation in high temperature applications.

The upper operating temperature of optical modules may be limited by the lifetime of the lasers and/or the light emitting diodes (LEDs) used in the modules. For example, the lifetime may be limited by long term wear out. The upper operating temperature of optical modules may be extended by using devices that are capable of operating at high temperatures and using heat sinking. The upper operating temperature of optical modules may also be extended by operating the devices with the minimum possible bias current. For relatively low-speed applications (below 1 Gbps), optical modules may be conceived and implemented with the capability to operate in ambient temperatures as high as 150° C. The lifetimes (mean-time-to-failure or “MTTF”) of such devices may be thousands to ten thousands of hours. These lifetimes may be sufficient for some applications. However, many applications, such as deep-hole oil drilling and jet engine control, require operating temperatures of 175° C. or even higher. Current technology does not provide a way of achieving these temperatures with sufficient optical module lifetime as the laser and/or LED lifetime may be severely degraded due to the inherent physics that cause laser degradation, such as migration of defects. Thermoelectric coolers may be a potential solution; however, these devices also lack the ability to operate reliably at very high temperatures.

SUMMARY OF THE INVENTION

To this end, an apparatus having an optically and electrically pumped semiconductor laser or light emitting diode (LED) is provided. The apparatus may also have a semiconductor light source and electrical current injection. The apparatus also may have an optical fiber and a pump light source at a remote location. Finally, the apparatus may have optics at the semiconductor laser configured to couple light from the optical fiber into the semiconductor laser for optical pumping and to couple light from the semiconductor laser into the same or a different optical fiber.

In an embodiment, the pump light source may be a semiconductor having a wavelength suitable for optically pumping the semiconductor light source.

In an embodiment, the optical fiber may be a single mode fiber or a multimode fiber.

In an embodiment, the optical fiber may be glass or may be polymer.

In an embodiment, the temperature at the semiconductor light source may not be conducive to the required reliability with only electrical biasing and modulation.

In an embodiment, the pump light source may be located in a remote location where the temperature is conducive to the required reliability with electrical biasing.

In an embodiment, the semiconductor light source may be biased with optical pumping and modulated with electrical current injection.

In an embodiment, the modulation by electrical current injection may be digital data and/or analog data.

In an embodiment, the electrical current injection may be a portion of the total bias.

In an embodiment, the electrical current injection results in a direct current bias conducive to the required reliability of the semiconductor light source at its ambient temperature.

In an embodiment, the optical pumping to bias the semiconductor light source may avoid resistive heating associated with electrical bias currents.

In an embodiment, the optics may also have a beam splitter.

In an embodiment, the semiconductor light source may be one or more of the following: a light emitting diode (LED), a vertical-cavity surface-emitting laser (VCSEL), a Fabry-Perot laser, and/or a distributed feedback (DFB) laser.

In another embodiment of the invention, a method of optically and electrically pumping a semiconductor light source is provided. The method may have the steps of: supplying an electrical current injection to the semiconductor light source; configuring optics at the semiconductor light source to couple light from the semiconductor light source into an optical fiber; providing a pump light source at a remote location; and configuring optics to couple light from the pump light source into the same or a different optical fiber for optical pumping of the semiconductor light source.

In an embodiment, the method may have the step of arranging a beam splitter at the pump light source to couple a portion of the light from the pump light source into the optical fiber for optical pumping of the semiconductor light source.

In an embodiment, the method may have the step of selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source.

In an embodiment, the method may have the step of modulating the semiconductor light source with electrical current injection.

In an embodiment, the modulation of the semiconductor light source with electrical current injection may be used to transmit data optically.

In an embodiment, the semiconductor light source may be directly modulated using the electrical current injection.

In an embodiment, the modulation of the semiconductor light source may be for the purpose of data transmission.

In an embodiment, the method may have the step of biasing the semiconductor light source with optical pumping.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a VCSEL with hybrid optical and electrical pumping for achieving reliable operation at high temperatures in accordance with the embodiments disclosed herein.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor laser and/or LED may be biased using optical pumping and may be directly modulated using a relatively small electrical current that may be used to convert the incoming electrical signal into an optical signal. An optical fiber may be used to provide the light for biasing the laser via optical pumping, as well as collect the modulated optical signal for data transmission. The light source for optically pumping the laser may be of a wavelength that may be absorbed by the active region of the laser and may be a shorter wavelength than that of the optical signal emitted by the laser.

FIG. 1 is a schematic diagram of an embodiment of an apparatus having a VCSEL with hybrid optical and electrical pumping for achieving reliable operation at high temperatures. In particular, an apparatus 10 may have a VCSEL 20 fabricated on a VCSEL substrate 30. While FIG. 1 illustrates a VCSEL 20, the invention is not intended to be limited to only a VCSEL. Any semiconductor light source may be used. A light beam 40 may be coupled by optics 45 into and/or out of an optical fiber 50. The optical fiber 50 may have a first end 51 and a second end 52. The second end 52 of the optical cable 50 may be remotely located a distance from the first end 51 of the optical cable 50. The light beam 40 may be bidirectional as indicated in FIG. 1. The VCSEL 20 may provide an optical signal 55 that may be carried in the optical fiber 50. Thus, the light beam 40 may comprise the optical signal 55 emitted from the VCSEL 20 and an optical pump 75 emitted by the optical pump source 70. The optics 45 may comprise a coupling lens and/or the like.

The apparatus 10 may also have a beam splitter 60 located remotely at the second end 52 of the optical fiber 50. The apparatus 10 may also have an optical pump source 70. The optical pump source 70 may provide the optical pump 75 of a particular wavelength. The wavelength may be selected to efficiently pump the VCSEL 20. The bidirectional light beam 40 may also have the optical pump 75 from the optical pump source 70. The optical pump 75 from the optical pump source 70 may be used to bias the VCSEL 20. The beam splitter 60 may be used to spatially separate the optical pump 75 of the optical pump source 70 and the optical signal 55 from the VCSEL 20. The beam splitter 60 may enable the single optical fiber 50 to carry both the optical pump beam 75 and the optical signal 55. Although the use of a single optical fiber is shown in FIG. 1, the invention is not intended to be limited to the use of a single optical fiber and is intended to include the use of separate optical fibers for the optical pump and the optical signal eliminating the need for the beam splitter. In addition, optical pumping of the semiconductor laser can be achieved in a variety of ways including vertical illumination from the top or through the substrate, as well as laterally through the side or ends of the semiconductor laser source. The invention is intended to include these configurations and is not intended to be limited to the specific configuration shown in FIG. 1. The apparatus 10 may enable the optical pump source 70 and the optical receiver of the optical link to be placed remotely in a lower temperature environment, while the data generated in the high temperature environment may be transmitted optically over the optical fiber 50 by directly modulating the VCSEL 20. The apparatus 10 also may have an electrical current injection 90 supplied to the VCSEL 20 to provide modulation of the VCSEL 20. At low modulation speeds, the modulation current provided by the electrical current injection 90 may be substantially lower than that required for biasing the VCSEL 20 or directly modulating the VCSEL 20 at high speeds.

For lasers where optical facet damage is not a limiting factor, such as VCSELs, the lifetime of the laser may be primarily determined by two factors. For example, one factor may be an exponential dependence of the lifetime on junction temperature. Another determining factor may be a factor that varies with approximately the square of the current. Thus, the modulation current provided by the electrical current injection 90 may play a major role in extending the lifetime of the laser. While very high operating temperatures may still have a substantial negative effect on laser lifetime, substantially reducing the operating current may have a significant positive effect on laser lifetime, enabling laser lifetimes adequate for operation in many applications, such as deep-hole oil drilling and jet engine control, where operation is not currently possible.

It should be understood that various changes and/or modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and/or modifications may be made without departing from the spirit and/or scope of the present invention and without diminishing its attendant advantages. It is, therefore, intended that such changes and/or modifications be covered by the appended claims. 

1. An apparatus, comprising: a semiconductor light source; a pump light source located remotely relative to the semiconductor light source wherein the pump light source produces an optical pump beam; an optical fiber positioned between the semiconductor light source and the pump light source wherein the optical fiber has a first end and a second end wherein the second end is located a distance from the first end; optics arranged at the semiconductor laser wherein the optics are configured to couple light from the semiconductor laser into the first end of the optical fiber and to couple the optical pump beam from the pump light source from the second end of the optical fiber into the semiconductor laser for optical pumping; and an electrical current injection supplied to the semiconductor light source wherein the semiconductor light source is electrically pumped by the electrical current injection and further wherein the semiconductor light source is optically pumped by the optical pump beam.
 2. The apparatus of claim 1 further comprising: a beam splitter located adjacent the second end of the optical fiber.
 3. The apparatus of claim 1 wherein the pump light source is a semiconductor laser having a wavelength selected to optically pump the semiconductor light source.
 4. The apparatus of claim 1 wherein the optical fiber comprises a single mode fiber, a multimode fiber, glass or polymer.
 5. The apparatus of claim 1 wherein the semiconductor light source is biased with optical pumping and modulated by the electrical current injection.
 6. The apparatus of claim 1 wherein the semiconductor light source is modulated by electrical current injection wherein modulation is digital data or analog data.
 7. The apparatus of claim 1 wherein the electrical current injection is a portion of the total bias of the semiconductor light source.
 8. The apparatus of claim 1 wherein the electrical current injection results in a direct current bias of the semiconductor light source conducive to the required reliability of the semiconductor light source at its ambient temperature.
 9. The apparatus of claim 1 wherein the optical pump beam biases the semiconductor light source without significantly heating the semiconductor light source.
 10. The apparatus of claim 1 wherein the semiconductor light source comprises a light emitting diode (LED), a vertical-cavity surface-emitting laser (VCSEL), a Fabry-Perot laser, or a distributed feedback (DFB) laser.
 11. A method of optically and electrically pumping a semiconductor light source, the method comprising: supplying an electrical current injection to the semiconductor light source; configuring optics at the semiconductor light source to couple light from the semiconductor light source into an optical fiber; providing a pump light source at a remote location; and configuring the optics to couple light from the pump light source into the optical fiber for optical pumping of the semiconductor light source.
 12. The method of claim 11 further comprising: arranging a beam splitter at the pump light source wherein the beam splitter couples a portion of the light from the pump light source into the optical fiber for optical pumping of the semiconductor light source.
 13. The method of claim 11 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source.
 14. The method of claim 11 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source wherein the wavelength is selected to be absorbed by an active region of the semiconductor light source.
 15. The method of claim 11 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source wherein the wavelength is selected to be a shorter wavelength than that of an optical signal emitted by the semiconductor light source.
 16. The method of claim 11 further comprising: modulating the semiconductor light source with the electrical current injection.
 17. The method of claim 11 further comprising: biasing the semiconductor light source with optical pumping.
 18. The method of claim 11 further comprising: providing the semiconductor light source at a first location having a first ambient temperature; and providing the pump light source at the remote location having a second ambient temperature wherein the second ambient temperature is less than the first ambient temperature.
 19. The method of claim 16 further comprising: generating data in the first location having the first ambient temperature; and optically transmitting the data over the optical fiber by directly modulating the semiconductor light source.
 20. An optical link system comprising: a semiconductor laser biased using optical pumping and directly modulated using an electrical current wherein the electrical current is used to convert an incoming electrical signal into an optical signal; a light source having a wavelength for optically pumping the semiconductor laser wherein the wavelength is absorbed by an active region of the semiconductor laser and is a shorter wavelength than that of the optical signal emitted by the semiconductor laser; and an optical fiber configured and arranged to provide light from the light source for biasing the semiconductor laser via the optical pumping wherein the optical fiber transports the modulated optical signal for data transmission.
 21. A method of optically and electrically pumping a semiconductor light source, the method comprising: supplying an electrical current injection to the semiconductor light source; configuring optics at the semiconductor light source to couple light from the semiconductor light source into a first optical fiber; providing a pump light source at a remote location; and configuring optics to couple light from the pump light source into a second optical fiber at the remote location and configuring optics for coupling the pump light source into the semiconductor light source from the second optical fiber for optical pumping of the semiconductor light source.
 22. The method of claim 21 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source.
 23. The method of claim 21 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source wherein the wavelength is selected to be absorbed by an active region of the semiconductor light source.
 24. The method of claim 21 further comprising: selecting a wavelength of the pump light source suitable for optically pumping the semiconductor light source wherein the wavelength is selected to be a shorter wavelength than that of an optical signal emitted by the semiconductor light source.
 25. The method of claim 21 further comprising: modulating the semiconductor light source with the electrical current injection.
 26. The method of claim 21 further comprising: biasing the semiconductor light source with optical pumping.
 27. The method of claim 21 further comprising: providing the semiconductor light source at a first location having a first ambient temperature; and providing the pump light source at the remote location having a second ambient temperature wherein the second ambient temperature is less than the first ambient temperature.
 28. The method of claim 25 further comprising: generating data in the first location having the first ambient temperature; and optically transmitting the data over the optical fiber by directly modulating the semiconductor light source.
 29. An optical link system comprising: a semiconductor laser biased using optical pumping and directly modulated using an electrical current wherein the electrical current is used to convert an incoming electrical signal into an optical signal; a light source having a wavelength for optically pumping the semiconductor laser wherein the wavelength is absorbed by an active region of the semiconductor laser and is a shorter wavelength than that of the optical signal emitted by the semiconductor laser; a first optical fiber configured and arranged to provide light from the light source for biasing the semiconductor laser via the optical pumping; and a second optical fiber wherein the optical fiber transports the modulated optical signal for data transmission. 